1. Field of the Invention
The present invention relates generally to devices and methods for delivering implants or performing procedures at sites within intervertebral discs or adjacent vertebral endplates, and more specifically to devices and methods for delivering implants through a posterior aspect of a vertebral body such as a pedicle or performing a procedure into the anterior aspect of the spinal column.
2. Background of the Related Art
Surgery for spine fusion or stabilization generally involves using implants and instrumentation to provide support to the affected area of the spine while allowing the bones thereof to fuse. The technology initially evolved using bone chips around and on the top of an area of the spine that had been roughened to simulate a fracture in its consistency. The area, having encountered the bone chips, would then proceed to heal like a fracture, incorporating the bone chips. However, surgical procedures dealing with the spine present notable challenges. For example, bioengineers have been required to identify the various elements of the complex motions that the spine performs, and the components of the complex forces it bears. This complexity has made it difficult to achieve adequate stability and effective healing in surgical procedures directed to the spine.
One surgical technique provided by Cloward, involves cutting a dowel type hole with a saw across or through the moveable intervertebral disc and replacing it with a bone graft that was harvested from the hip bone. This procedure results in a fusion of the adjacent vertebral bodies and limits motion and mobility. However, as a result of the complex motions of the spine, it is often difficult to secure the dowel from displacing. Further, it has become apparent over time, however, that this particular technique does not always yield a secure fusion.
Other techniques have been developed that involve the placement of various hardware elements, including rods and hooks, rods and screws and plates and screws. The dowel technique also has advanced over the past ten to fifteen years or so, with dowels being fabricated from cadaver bone or metals such as titanium or stainless steel. These techniques, whether using hardware, dowels or some combination thereof, have a common goal to enhance stability by diminishing movement, thereby resulting in or enhancing the potential of a fusion of adjacent vertebral bones. For example, in one of these other techniques, the disc is removed and adjacent vertebrae are positioned in a stable position by placing a plate against and traversing them, which plate is secured or anchored to each by means of screws. A disadvantage of such procedures is the use of components that protrude outwardly, which may contact and damage a body part, such as the aorta, the vena cava, the sympathetic nerves, the lungs, the esophagus, the intestine and the ureter. Also, many constructions involve components that may loosen and cause undesirable problems, often-necessitating further surgical intervention.
In another procedure, cages in the form of two parallel circular or rectangular devices are made out of a material such as titanium or stainless steel and these devices are fenestrated. Bone is packed in the center of the devices that will heal to adjacent bone through each fenestration. In this procedure, the disc space is distracted so all ligamentous structures are taut and the bones are held in their normal maximal position of distraction. Because the cages are implanted in spongy bone, they are more likely to collapse into the surrounding bone, thus resulting in loss of distraction and subsequently cage loosening and dislodgment.
U.S. Pat. No. 5,591,235 discloses a spinal fixation device and technique for stabilizing vertebrae. In this technique, a hollow screw is inserted into a hole, preferably a hole saw recess, in each adjoining vertebrae. A channel is cut into the vertebrae, which is lined up with corresponding axial slots in the screw. A rod is inserted into the channel and so as to pass through the axial slots in the screw. The rod is secured to each of the screws by means of a locking cap. The rod also is arranged so as to provide a bridge between the hollow screws in the adjoining vertebrae. Certain disadvantages have been surmised using such a device and technique. For example, it has become apparent that the trough in the vertebral bodies destabilizes some of the cortex of the vertebrae body wall, which is the strongest component.
In addition to fixation or fusion of vertebral columns, the prior art also describes methods or other spinal repair procedures, such as discectomy wherein an artificial disc or prosthetic device is placed within the vertebrae of the spine. For such prior art methods and related devices, there have been short comings such as having difficulty in securing and maintaining the prostheses within the vertebral space or resulting in significant modification or damage to the load bearing surfaces of the vertebrae in an effort to secure the prosthesis.
Another method or other spinal repair technique involves augmentation of the nucleus of an intervertebral disk of the spine. The intervertebral disk is a flexible cartilaginous structure that is disposed between adjacent vertebrae. These disks form joints between the bodies of the vertebrae, which serve to unite adjacent vertebrae and to permit movement between them. These disks also play a role as shock absorbers when force is transmitted along the vertebral column during standing and movement.
Each intervertebral disk is formed of two parts, a central mass called the nucleus pulpsous (herein the nucleus) and a surrounding fibrous layer, the annulus fibrosus (herein the annulus). The nucleus has a semi-gelatinous consistency, which allows it to become deformed when pressure is placed upon it, enabling the disk to change shape as the vertebral column moves and acts in a hydrostatic manner. The top and bottom of the disc are supported by relatively bony endplates.
There is described in U.S. Pat. Nos. 5,047,055; 5,824,093 6,264,695; the teachings of which are incorporated herein by reference, various techniques and/or prosthetics for use in replacing or augmenting a spinal disc nucleus. Given the structure of the disk and its location between adjacent vertebrae, it is not s simple task to access the nucleus for the insertion of such prosthetics or materials to augment the nucleus. One technique for accessing the nucleus contemplates using the defect in the annulus, however, in practice the defect usually needs to be enlarged to allow the insertion of the prosthetic. Another technique contemplates having the surgeon drill through one of the adjacent bodies using a lateral approach. This technique relies heavily on the skill and dexterity of the surgeon not to damage surrounding tissues, nerves and blood vessels. Also, the hole formed by such drilling is not easily sealed because of its shape and configuration.
Various implants, fusion devices, cages, and the like may be used to treat pathological vertebral bodies and intervertebral discs are known in the art. Certain physiological environments present challenges to precise and minimally invasive delivery. Also, the difficulty and danger of the typical implantation procedure itself, due to the proximity of the aorta (if an anterior approach is used) and the spinal cord (if a posterior approach is used), limits the size and ease of placement of the implant. In light of the inherent limitations involved with delivery of medical devices to the disc environment, safer and less invasive surgical approaches are desired.
Therefore, there is a need for an apparatus and method for delivering implants through a posterior aspect of a vertebral body such as a pedicle and placing the implant or performing a procedure into the anterior aspect of the spinal column. There is also a need for implants which do not protrude from the vertebral body and provide stable support to the spine.